The use of organotin compounds has grown rapidly since their commercialization in 1936 both in terms of quantity and scope. These compounds are widely used in such areas as stabilizers for plastics including polyvinyl chlorides (PVCs), industrial catalysts, pesticides, antimicrobials and wood preservatives. Since the 1960's, tributyltin (TBT) has been added to paint coatings for ships and marine structures as antifouling agents to prevent underwater creatures from attaching themselves. There has been growing concerns, however, about the harmful nature of organotin compounds since many of these are toxic and able to disrupt normal growth even when traces are released into the ecosystem. Tributyltin, a representative organotin pollutant of the sea, is polluting marine ecosystems on a global scale. It has been reported to inhibit the growth of oysters, mussels and bivalves. Since the early 1980's, tributyltin has been also known to cause imposex in gastropods, in which formation of male genitalia occurs in females accompanied with a loss of reproductive function. Meanwhile, other toxic organotin compounds such as triphenyltin and tricyclohexyltin are causes for concern as well.
The diplomatic conference held in October, 2001 at the international maritime organization (IMO) has adopted the antifouling system (AFS) convention that regulates the use of TBT antifouling agents on ships. Taking momentum from this convention, the Korean government is in the process of incorporating the contents of this convention into domestic law.
Already, the Ministry of Environment of Korea issued an announcement (No. 2003-163, Sep. 16, 2003) listing antifouling paints containing tributyltin as “chemicals of which production, import or use are either banned or subject to restrictions”. In addition, a total ban on tributyltin-containing antifouling paints has been in effect since Nov. 13, 2003 for all ships registered in Korea including ocean liners and deep-sea fishing vessels.
As described above, organotin compounds can cause severe damage to ecosystems and their concentrations in the environment constantly vary according to biological (e. g., metabolism) and non-biological (season, ocean currents) factors. However, research has been lacking on apparatuses and methods for a facile, accurate and continuous determination of these compounds. At the moment, there are no patent applications directed to systems or methods for determining organotin compounds in Korea.
Although there are some methods of analysis available for quantitating organotin compounds in liquid samples (titration, gas chromatography, etc.), none of these methods have been automated so far. Gas chromatography (GC) is the method most generally used among these. For instance, U.S. Pat. No. 4,610,169 describes an apparatus for concentrating organotin compounds in gaseous samples by means of a variable temperature trap for determining organotin levels. Apparently, this still leaves a strong need for a measuring device that does not require such pretreatment steps. An article from the Journal of Analytical Atomic Spectrometry (vol. 17 (2002), pp 824-830) discloses a method based on gas chromatography and mass spectrometry for mono-, di- and tributyltin in seawater. This method involves the cumbersome step of extraction with organic solvents for gas chromatography and mass spectrometry analyses. In addition, since this method requires a tin isotope 119Sn for analysis, it can be costly. In US patent publication No. 2006/0276666, a method for treating liquid samples contaminated with organotin compounds, organotin compounds are likewise extracted with organic solvents followed by gas chromatography for the evaluation of decontamination efficiency. Meanwhile, the Korean official test method for marine environment describes a GC-based method for determining levels of organotin compounds. In this method, organotin compounds from samples are extracted with methylene chloride, concentrated and derivatized with Grignard reagents, followed by filtration through a Florisil® column to remove interfering substances. This column eluate is then subject to separation with GC and finally the components are detected using a flame photometric detector (FPD).
Although gas chromatography, as shown above, is the conventional method for analyzing organotin compounds, it has important shortcomings as well. GC involves various, complicated pre-treatment steps which are cumbersome to manual operators, making automation a difficult goal. In addition, losses can occur during the stages of extraction and concentration and such manual operations are prone to wide variation in data quality depending on the operator. Furthermore, GC equipments are costly. Considering the extremely small quantities of analyte samples injected in GC, the reliability of data obtained from GC is further diminished when such shortcomings as mentioned above are taken into account.
Even if methods other than GC were available for determining organotin levels so that the shortcomings associated with GC could be overcome, such methods would still suffer from their inability to continuous concentration measurements as well as wide discrepancies in measurements arising from the different capabilities of individual operators as long as they involve unautomated steps including pre-treatment of samples. Thus, the demand for automated systems capable of an accurate, continuous and convenient determination of trace levels of organotin in liquid samples still remains unanswered.